The present invention relates to an optical disk device, a circuit, or an IC (semiconductor integrated circuit device) provided for the optical disk medium, for optically reproducing (reading) or recording a signal (data/information) from/to an optical disk medium.
In a related art optical-disk device technique, a flaw or a defect (which will be abbreviated merely to defect, hereinafter) is coped with by controlling the optical disk device in such a manner that the device is put in a state immediately before passage of the defect on the disk after the defect passage under servo control.
There is such a description in Jp-A-2000-90467 that, when a large fluctuation component is included in a servo error signal immediately before generation of a defect detection signal (defect signal), a servo hold signal including a signal opposite in polarity to the servo error signal immediately after the generation of the defect detection signal is generated, the reading operation of a pickup is controlled according to the servo hold signal in place of a servo drive signal during the generation of the defect detection signal, which results in that, even after a reading point passes through the location of the defect on a recording medium, a servo state immediately before the passage of the defect can be maintained.
In a control system upon the defect detection in the related art, however, when a large fluctuation component before the defect detection is supplied to an actuator as a hold signal which involves the fluctuation component but which has the opposite polarity after the defect detection and an objective lens is correspondingly moved, the magnitudes of the fluctuation components are cancelled each other. However, an acceleration caused by the large fluctuation component before the defect detection is not exactly the same as an acceleration caused by the fluctuation component having the polarity opposite thereto. As a result, the objective lens is moved at a uniform velocity under control of the hold signal during the defect passage. Thus the related art has a problem that the objective lens cannot maintain a servo state immediately before the defect passage, that is, a position before the defect passage.